An all-atom kinetic Monte Carlo model for chemical vapor deposition growth of graphene on Cu(1 1 1) substrate.

Various graphene morphologies (compact hexagonal, dendritic, and circular domains) have been observed during chemical vapor deposition (CVD) growth on Cu substrate. The existing all-atom kinetic Monte Carlo (kMC) models, however, are unable to reproduce all these graphene morphologies, suggesting that some crucial atomistic events that dictate the morphology are missing. In this work, we propose an all-atom kMC model to simulate the graphene CVD growth on Cu substrate. Besides the usual atomistic events, such as the deposition and diffusion of carbon species on the substrate, and their attachments to the edge, we further include three other important events, that is, the edge attachment of carbon species to form a kink, the diffusion of carbon species along the edge, and the rotation of dimers to form kinks. All the energetic parameters of these events are obtained from first-principles calculations. With this new model, we successfully predict the growth of various graphene morphologies, which are consistent with the morphology phase diagram. In addition to confirming that carbon dimers are the dominant feeding species, we also find that the dominance level depends on the growth flux and temperature. Therefore, the proposed model is able to capture the growth kinetics, providing a useful tool for controlled synthesis of graphene with desired morphologies.

Revealing the Grain Boundary Formation Mechanism and Kinetics during Polycrystalline MoS2 Growth.

Controllable synthesis of MoS2 with desired grain morphology via chemical vapor deposition (CVD) or physical vapor deposition (PVD) remains a challenge. Hence, it is important to understand polycrystalline growth of MoS2 and further provide guidelines for its CVD/PVD growth. Here, we formulate a kinetic Monte Carlo (kMC) model aiming at predicting the grain boundary (GB) formation in the CVD/PVD growth of polycrystalline MoS2. In the kMC model, the grain growth is via kink nucleation and propagation, whose energetic parameters and initial nucleus details are either from first-principles calculations or from experiments. Using the kMC model, we perform extensive simulations to predict the GB formation by using two, three, four, and five initial nuclei and compare the simulation results with previous experimental results. The obtained GB morphologies are in an excellent agreement with those experimental results. These agreements suggest that the proposed kMC model can correctly capture the mechanism and kinetics of GB formation. In particular, we reveal that the formation of smooth/rough GB is dictated by the two growth vectors for the kink propagation at the two associated grain edges, which is validated by our high-resolution scanning transmission electron microscopy images for PVD growth of MoS2 grains. Besides, we have made predictions beyond reproducing experimental observations, including the growth with artificially designed nuclei, the morphology transformation by tuning the Mo and S sources, and the formation of high-quality single-crystalline monolayer MoS2 by using single-crystalline substrates with vicinal steps. Our kMC model may serve as a powerful predictive tool for the CVD/PVD growth of monolayer MoS2 with desired GB configurations.